Mesmero, I mean. When did Pyro come back, and was it ever explained how? I guess that he stayed after Necrosha. Is the the real Avalanche, or is this a new guy?

Mesmero: No explanation.

Pyro: No explanation, but Necrosha would be a good one. He's certainly not acting like the old Pyro was before his "death."

Avalanche: New guy. We get his backstory in this issue. He's a new mutant, a college student named Simon (no last name yet). He was at the library several months ago when his powers first manifest, and Mesmero pretended to be Xavier to recruit him.